The present invention concerns the field of electronics in the area of displacement sensors used in systems for controlling movements and alarms.
The displacement sensors already available in the market are very numerous and use various principles for detecting the displacement, but are for the most part associated with common inconveniences and drawbacks, cases in point being high costs, operational instability at low and high temperatures, sensitivity to such external factors as radio interference, noises, magnetic fields, low mechanical resistance to impact and vibrations, difficult assembly due to the need for installing the sensor in a clearly defined angular position.
The displacement sensor patented by the present applicant in 1983 (Italian Patent No. 1.175.163) comprises a ball in a spherical chamber struck by a beam of ultrasounds that are received and reflected at a constant frequency for as long as the chamber is not moving and reflected at variable frequencies when the chamber, and therefore also the ball, have carried out some movement; this sensor is associated with some of the disadvantages set out above, in particular instability of performance when operating in extremely high or low temperatures or in the presence of external interferences.
The following terms will be conventionally employed in the description that follows:
i) ballxe2x80x94a body of substantially spherical shape;
ii) chamberxe2x80x94a hollow and preferably spherical chamber;
iii) quantity of lightxe2x80x94the entity that in physics is defined as the product of the light flux and its duration and which, for the purposes of the present technical invention, may also be understood as the entity that in physics is defined as light intensity, that is to say, as the ratio between the light flux and the solid angle at which the said flux is moving.
The present invention obviates the drawbacks described above; it is a sensor that in a known manner comprises a ball inserted in a chamber which comprises first and second passages both communicating with the outside and wherein the ball generally finds itself in a state of stable equilibrium, ready to move at even the slightest movement of the chamber and, as characterized in the claims, comprises a source of visible light placed outside the chamber and positioned in such a manner as to illuminate the interior of the chamber through the first of the said passages and an element sensitive to the quantity of light reflected to the outside of the chamber through the second passages (element that hereinafter is to be referred to, more simply, as xe2x80x9clight-sensitive elementxe2x80x9d) to detect the said quantity of light, convert it into an electric signal and transfer the said signal to an electronic circuit associated with the sensor, the said electronic circuit being capable of analyzing the said signal, comparing it with pre-selected parameters and deciding whether or not it is to generate at least one pulse that activates a movement control system of the means in which the sensor is installed and activates an alarm system.
The light-sensitive element receives a constant quantity of light reflected by the ball and the interior wall of the chamber for as long as the ball remains still into the chamber or for as long as the atmospheric conditions within the chamber remain constant, while a movement of the ball or changed atmospheric conditions within the chamber will cause a different quantity of light to be reflected onto the light-sensitive element; the latter, in association with the electronic circuit, checks whether the light quantity it has received still falls within a predefined interval; if this quantity is no longer within the said interval, the system sends at least one signal to the location and in the conditions required to trigger the desired control action of the means and the alarm action.
The implementation just described above, which comprises a light source that emits a constant quantity of visible light, is suitable for cases in which the sensor is applied to a means that is in a permanent state of rest, as is the case, for example, of a sensor applied to some fixed structure, such as a rock face or a slope: for as long as the light conditions within the chamber and the quantity of light reflected onto the light-sensitive element remain within the aforesaid interval, the system will not trigger any alarm action.
Preferably, the quantity of visible light emitted by the light source is controlled by a balancing unit comprised in the electronic circuit and comes into operation at the very moment in which an operator activates the sensor applied to the means in question; the said balancing unit will cause the quantity of light emitted by the light source to vary in such a manner as to bring the quantity of light reflected onto the said light-sensitive element back to an appropriately pre-selected value whenever the variations of the said reflected light are due to slow displacements of the chamber or to changes of the atmospheric conditions within the chamber and will do so independently of the inclination at which the sensor is mounted on the means in question; this implementation is suitable, for example, for the case of movements caused by the digging into the asphalt surface of a motorcycle stand or by the deflation of a tyre of a car.
It will readily be understood that the balancing unit will perform its function irrespective of the position in which the sensor is applied, even when its inclination is far removed from the one that could be said to be a normal inclination, like the one in which the longitudinal axis of the chamber is horizontal; for example, if the sensor, for reasons of space, were to be mounted rotated through 180xc2x0 with respect to its normal inclination or if the motor vehicle were to be parked on a strongly sloping road. In such conditions the balancing unit will cause the light quantity emitted by the light source to vary in such a way as to bring the quantity of light received by the light-sensitive element back to the appropriately pre-selected value.
The principal advantages of this sensor are its limited cost, its operating stability at temperatures comprised within a wide interval, for example, between +8 C. and xe2x88x9240xc2x0 C., and its considerable mechanical sturdiness.
The performance of the invented sensor renders it capable of an enormous number of uses that can range from the protection of motor vehicles, the control of movements of the ground, dams, glaciers, buildings (about earthquakes), floating jetties and the alarm systems associated therewith.
When integrated into motor vehicle alarm systems, in particular, the sensor finds an optimal application in the detection of unauthorized displacements. The system, of course, will be calibrated in such a way as not to trigger any alarm in case of the ball undergoing some accidental movement, that is to say, whenever the movements of the ball do not exceed a predetermined number of movements in a predetermined time.